1. Field
The present disclosure relates to a method for synthesizing a hydrocarbon-based electrolyte polymer and a polymerization solvent used therein.
2. Description of the Related Art
Properties required for an electrolyte membrane for a polymer electrolyte fuel cell may include a high proton conductivity, high mechanical properties, a low fuel permeability, a high dimensional stability, high inert characteristics and low cost.
As an electrolyte membrane for a polymer electrolyte fuel cell according to the related art, fluorocarbon-based electrolyte polymer membranes such as Nafion®, Flemion®, Aciplex™ membranes etc. are known. Although such membranes have a high proton conductivity, high inert characteristics and good mechanical properties, a high fuel permeability, a low proton conductivity under the conditions of low-moistening and high temperature and particularly high cost are still problematic.
Thus, low cost hydrocarbon-based electrolyte polymers which may substitute for the fluorocarbon-based electrolyte polymers have been developed. Typically, the hydrocarbon-based electrolyte polymers applied to fuel cells have been obtained by a direct polycondensation of aromatic ether bond-containing polymers, such as polyarylene ether sulfone or polyarylene ether ketone, using a sulfonated monomer.
Such a direct polycondensation method essentially requires a process of inducing ether bonds between monomers. Particularly, during the process, an azeotropic mixing solvent including a low-boiling point solvent, such as dimethyl acetamide, N-methylpyrrolidone or dimethyl sulfoxide, and a high-boiling point solvent, such as toluene or cyclohexane, may be used to induce a dehydration. However, the use of such an azeotropic mixture may lower a solubility of monomers required for polymerization, thereby making it difficult to carry out a homogeneous polymerization and causing a polymerization reproducibility problem.
To address the problems, there has been suggested a technique using a dimethyl acetamide allone as a polymerization solvent instead of the azeotropic solvent (Korean Patent Laid-Open No. 2013-0106558). In the technique, a polymerization is carried out under a single polymerization temperature without using a complicated polycondensation adopting the azeotropic solvent, such as toluene, and the polymerization solvent.
However, according to an observation by the inventors of the present disclosure, such technique is not amenable to a mass production, because a long reaction time is required to obtain a desired molecular weight of polymer. Thus, the technique is still required to be improved.